1. Technical Field
Exemplary aspects of the present disclosure generally relate to an image forming apparatus, and more particularly to an image forming apparatus such as a copier, a facsimile machine, a printer, a plotter or a multi-functional system including a combination thereof.
2. Description of the Related Art
Generally, known tandem-type color image forming apparatuses adjust color drift by forming on an intermediate transfer belt a test pattern for detecting the color drift in each color and detecting the position of the test pattern by a reflective-type photosensor or the like. Based on the detection result of the photosensor, an amount of color drift in each component such as registration, magnification, and skew is calculated. In accordance with the calculation result thus obtained, an optical path of an optical system, a start position of image writing for each color, and a pixel clock frequency are corrected. In order to increase detection accuracy, for example, the test patterns are formed at a plurality of transfer positions, for example, at the center and at both ends of the intermediate transfer belt, and the amount of color drift is calculated.
Generally, in such image forming apparatus, at least one of a pair of secondary transfer rollers (for example, a drive roller and a secondary transfer roller) employs an elastic roller such as a rubber roller to enhance transferability. In this configuration, the diameter of the roller changes slightly between when the roller is pressed against a recording medium via the intermediate transfer belt during transfer of an image and when the roller is separated such as when the test pattern is formed for the color drift adjustment. When the diameter of the roller changes, the surface speed of the intermediate transfer belt entrained about the drive roller or the like fluctuates, hence resulting in a registration deviation in actual printing.